Federal authorities detained a 12th person in their investigation of a Russian spy ring in the United States, and he has been deported to Russia, U.S. law enforcement officials said Tuesday.

The man, Alexey Karetnikov, entered the United States in October and was living in the Seattle area, where he worked at Microsoft, according to federal officials and the company. Karetnikov, a Russian citizen in his early-to-mid-20s, had been held on immigration violations because there was insufficient evidence to charge him with a crime, the government officials said.

"He was just in the early stages; had just set up shop," said one senior federal law enforcement official, who spoke on the condition of anonymity because the details of the case were closely held. The official added that the FBI was monitoring the Russian almost immediately upon his arrival and that he had "obtained absolutely no information."

An immigration judge issued an order Monday for Karetnikov's removal from the United States, said Matt Chandler, a spokesman for the Department of Homeland Security. The Russian admitted he was illegally present in the country and agreed to the deportation in lieu of further court proceedings, said Chandler, who added that Karetnikov "would face criminal and civil penalties if he returned without express U.S. government permission.''

U.S. officials said Karetnikov was sent home Tuesday.

Database searches show that someone with Karetnikov's name had been living in an apartment in Redmond, Wash., since October. That man's Facebook page says he worked for Microsoft and a Romanian-based software company called Neobit.

Lou Gellos, a Microsoft spokesman, confirmed that Karetnikov had worked at the company for about nine months as a software tester. He said Karetnikov is the man whom authorities deported on Tuesday but would not comment further.

The latest detention added a new wrinkle to a case that has fascinated Americans since 10 people were arrested June 27 and charged with working as deep undercover Russian spies. The 10 sleeper agents pleaded guilty Thursday to acting as unregistered agents for Russia and were then "swapped" for four Russian prisoners in a deal reminiscent of the Cold War. An 11th man charged in federal court in New York remains at large.

Details about the 12th alleged spy came as information emerged on how the 10 agents involved in the swap are faring in Russia. Russian news media reported that they have applied to a witness-protection program and are seeking to change their names.

Moskovsky Komsomolets, a Russian newspaper, reported that the 10 agents are being debriefed at a Russian intelligence facility on the outskirts of Moscow. They are not allowed to leave the premises, but family members are allowed to visit, the newspaper said.

The reticence that most are showing might not apply to Anna Chapman, who became a tabloid sensation in the United States when sultry photographs of her were posted on the Internet after her arrest. Russian news media reported that Chapman is willing to sell her story to journalists.

Chapman had told her U.S. attorney, Robert M. Baum, that she may want to relocate to Britain, where the Russian acquired dual citizenship in 2002 through her marriage to a British businessman, Baum said Tuesday. But he said the British government has stripped Chapman of her citizenship and revoked her passport, citing the spy case.

In the United States, officials indicated last week that the case had effectively shut down the spy ring. But law enforcement officials said Tuesday that Karetnikov was not part of the same ring and had no direct ties to the other spies, although his name came up in the broader investigation.

It was unclear when Karetnikov was detained, although an official said he was in custody by last week. He was apparently not part of the swap because unlike the other 10 agents, he was not charged with a crime. One official said Karetnikov was "just doing the things he needed to do to establish cover," including holding down a job.

Asked whether further arrests are possible, one official said U.S. law enforcement authorities are closely monitoring all potential espionage activity but added, "I don't think there will be a 13th or a 14th arrest here."

Special correspondent Rebecca Omonira-Oyekanmi in London, special correspondent Julia Ioffe in Moscow, and staff writer Walter Pincus and research editor Alice Crites in Washington contributed to this report.